(a) Field of the Invention
The present invention relates to a method and apparatus for beam switching in a mobile communication network. More particularly, the present invention relates to a method and apparatus for beam switching in a mobile communication network using a millimeter wave (mmW) frequency band.
(b) Description of the Related Art
In general, for handover, a serving base station transmits a Radio Resource Control (RRC) connection reconfiguration message to a terminal to instruct a measurement control of the terminal. In this case, the RRC connection reconfiguration message includes measurement configuration information that sets measurement that the terminal is to perform.
The terminal measures Reference Signal Received Power (RSRP) or a Reference Signal Received Quality (RSRQ) based on measurement configuration information, and when RSRP or RSRQ of a neighbor cell is a threshold value or more, the terminal reports the measured RSRP or RSRQ value to a serving base station. Here, the RSRP represents average reception power of a cell-specific reference signal within a specific frequency bandwidth, and the RSRQ represents received reference signal quality. RSRP and RSRQ are used for a handover procedure in an RRC connected state, but RSRP is used for a cell selection or cell reselection procedure in an RRC idle state.
The serving base station determines whether to perform handover based on a measurement report from a terminal. When it is determined to perform handover, the serving base station transmits a handover request message to a target base station. Thereafter, the target base station performs admission control on whether to approve handover based on a handover request message. Therefore, even if a handover request of the serving base station exists, when approval of the target base station exists, handover is performed. For handover approval, the target base station transmits a handover request allowance message to the base station. The handover request allowance message includes handover approval information when handover is approved and handover rejection information when handover is rejected. When handover from the target base station is approved, the serving base station transmits a handover instruction message to the terminal to instruct handover. A phase from a handover determination time point to a time point that sends a handover instruction to a terminal is referred to as a handover preparation phase.
The terminal receives a handover instruction message and then performs an actual handover process. From this time, a handover execution phase is performed.
Thereafter, the terminal starts a procedure that performs handover from a serving base station to a target base station. The terminal performs a handover process after a random access procedure operation in a target base station to transmit a handover confirmation message to the target base station.
In such handover, even in frequent movement between beams within the same base station, because a handover procedure should be applied in an RRC layer corresponding to a layer 3 between base stations, there is a problem that a handover delay time increases. Further, because handover is always started by a base station, there is a problem that fast switching between beams is difficult and that a random access procedure should be performed using a Physical Random Access Channel (PRACH).